Wired broadband communication systems increasingly rely on fiber optical cables (fiber) for data transport. In the cable television environment, the network uses both fiber and coax (referred to as a “Hybrid Fiber-Coax” or “HFC” network). The signals run in fiber-optical cables from the cable head end to junctions near the subscriber (the “downstream” direction). At that point, the signal is converted from optical transmission over fiber to RF transmission over coaxial cables that run to a number of subscriber premises. These junctions are referred to as fiber nodes. Communications from the subscriber premises to the cable head end (the “upstream direction”) are sent over coax to the fiber node where the signal is converted from an RF signal to an optical signal. The optical signal is then sent over fiber to the cable head end.
Access to the cable network's data service is provided through a cable modem (CM). Increasingly, CMs are required to comply with an industry standard referred to as the “Data Over Cable Service Interface Specification” or DOCSIS. DOCSIS provides a set of standards and a certifying authority by which cable companies can achieve cross-platform functionality in Internet delivery. A DOCSIS-compliant cable network comprises a cable modem termination system (CMTS) that forms the interface to an Internet service provider (ISP) and exchanges digital signals with cable modems on a cable network.
Referring to FIG. 1, a block diagram of a DOCSIS-compliant HFC network is illustrated. In a DOCSIS HFC network, fiber node 105 is connected to CM FNi 101 and CM FNn 102 and fiber node 110 is connected to CM FN2i 103 and CM FN2n 104. Fiber nodes 105 and 110 communicate in the upstream direction with an upstream port 125 of a CMTS 120. A downstream port 150 on the CMTS 120 communicates in the downstream direction with the CM FN1i 101, CM FN1n 102, CM FN2i 103, and CM FN2n 104 through fiber nodes 105 and 110.
Communication between the CMTS 120 and fiber nodes 105 and 110 in both the upstream and downstream direction is over a fiber network. Communication between the fiber nodes 105 and 110 and their respective CMs is over coaxial cable.
Each time a CM is powered on (or booted), the CM registers with an upstream port on the CMTS. As an element of this registration process, the Media Access Control (MAC) address of the CM is communicated to the CMTS. Using the MAC address, the CMTS associates each CM with an upstream port on the CMTS to which the CM is connected.
In contrast to CMs, fiber nodes are not addressable today, and as a result, they are an invisible component on the HFC network. That is, while fiber nodes are connected to a CMTS, the CMTS cannot communicate directly with the fiber node. Since the fiber node represents a physical domain in the HFC plant, it is valuable to associate that domain with the logical domain in a network. Currently, information about the health and configuration of a fiber node is obtained from the HFC plant engineers responsible for configuring and maintaining the HFC.
Fiber nodes vary in configuration and are described in terms of the segmentation of the receivers in the forward (downstream) direction and transmitters in the reverse (upstream) directions. The segmentation of the node is a design consideration that is determined in part by the volume and nature of the subscriber traffic anticipated by the cable service provider.
By making the fiber node addressable, diagnostic information from the fiber node about the HFC plant can be reported in real-time to the CMTS. In addition, the number of subscribers connected to a fiber node is determinable in real-time by the CMTS. These data would be valuable in determining the demand on upstream ports of a CMTS and in managing available bandwidth and the most efficient segmentation of each fiber node. As new services are deployed (e.g., voice over IP), the need to manage the downstream network is even more critical to efficient management of network resources. Determining the capacity per node—per port in real-time would be invaluable in provisioning new customers and scaling for the future.
For example, when deploying voice over using the Internet protocol (VOIP) it is necessary for a multi-system cable operator (MSO) to accurately estimate the number of phone calls that a single upstream CMTS port may experience so as not to exceed the call capacity of the port. By determining the number of fiber nodes that can be served by a single upstream CMTS port (the “upstream channel combining ratio”), and the number of homes-passed per fiber node (a measure of potential subscribers), an MSO is able to assess how many “homes passed” are connected to that CMTS port. Knowledge of the volume of calls passing through a fiber node in “real time” would allow the MSO to determine when adjustments to the upstream combining ratio would be appropriate. The information would also be helpful in better focusing marketing and sales initiatives within a particular neighborhood by providing the MSO with information about unused capacity.
Making the fiber node addressable would also improve the ability of the network operator to diagnose and remedy network problems. In the case where there are problems on a DOCSIS CMTS upstream port, being able to associate that port with a fiber node would allow the operator to track the symptoms back to a specific area, identify what fiber node(s) are affected by the problem, and enhance the ability to dispatch technicians to the appropriate location.
U.S. patent application 2002/0136203 by Lira et al. (the “Lira Application”), teaches integrating the functionality of a CMTS into the fiber node. The integrated CMTS/fiber node includes a MAC layer that presumably allows the integrated CMTS/fiber node to be addressable. While the integrated CMTS/fiber node appears to offer some of the benefits of an addressable fiber node, the solution of the Lira Application introduces other problems. By distributing the CMTS functionality closer to the end devices (CMs), the number of CMTS rises to the number of fiber nodes on the network thus increasing the probability of CMTS failure and making maintenance more difficult. Additionally, incorporating the CMTS into the HFC plant exposes these sensitive electronics to the elements and provides more opportunity for tampering. (In a typical HFC network, the CMTS is located at a hub site, which site is environmentally controlled and secure.) Finally, in order to provide an addressable fiber node using the approach described in the Lira Application, current networks would have to be redesigned.
What is needed is a means of addressing existing and new fiber nodes in an HFC network and obtaining from the fiber node information about signal levels and other characteristics of the cable plant without increasing maintenance risks or modifying the architecture of existing networks. It would also be useful to be able to determine the traffic volume being handled by a fiber node to determine the demand on an upstream CMTS port and to permit adjustment of the upstream combining ratio would need to be made.